1. Field of the Invention
The present invention relates to an ignition timing controller suitable for use in a spark-ignition internal combustion engine, such as a gasoline engine, which may hereinafter be called merely the "engine".
2. Description of the Related Art
Control of the ignition timing of a gasoline engine has conventionally been conducted, for example, in the following manner. The ignition timing of the engine is controlled by determining the state of operation of the engine with a flow rate sensor adapted to detect the volume of intake air to the engine (a pressure sensor for detecting the pressure in an intake passage may be used instead of the pressure sensor) and an engine revolution number sensor adapted to detect the revolution number of the engine; determining, based on the state of operation determined from detection results by these sensors, basic ignition timing information in accordance with a two-dimensional map containing volumetric efficiencies E.sub.v (A/N) obtained by dividing the volumes A of intake air with engine revolution numbers N or advance values (information on ignition timing) determined from pressures of the intake passage and engine revolution numbers N; applying a suitable correction to the basic ignition timing information; and then actuating an ignition system, which generally includes a spark plug and an ignition coil, on the basis of the thus-obtained ignition timing information.
The above-described suitable correction to the basic ignition timing information includes a correction applied based on the coolant temperature of the engine, a correction effected in accordance with the intake air temperature, or the like. Since knock (knocking) occurs especially upon acceleration of the engine, it is also necessary to apply a certain correction to the ignition timing information upon acceleration of the engine.
Here, engine knock is an oscillation phenomenon in a combustion chamber, which is inducted by autoignition. Such knock produces an unpleasant noise and moreover, has a potential danger that it may adversely affect the engine.
With a view toward avoiding the occurrence of such knock, control has heretofore been performed to retard the ignition timing in general. In this case, it is difficult to detect any engine phenomenon which may lead to the occurrence of knock. Accordingly, a control method is adopted to retard the ignition timing to a safe side such that knock is not caused to occur even under worst conditions.